It is known that oxidation causes a deterioration of the flavor and odor of edible fats and oils, resulting in foods with unpleasant tastes and unappetizing odors. Many attempts have been made to combat this deterioration. Improvement in food preparation, refrigeration and packaging materials all help to retard oxidation but are not completely satisfactory or economically feasible in many instances. One solution to this problem is the use of food grade antioxidants such as butylated hydroxyanisole (BHA) and tocopherols which are introduced directly into the food products to inhibit the destructive processes which result in rancidity.
One measurement of performance of an antioxidant is the AOM Stability Test. Results of these tests show that the use of antioxidants can improve the oxidative stability of many foods, including animal fats and butters, coconut and palm kernel oils, essential oils and flavorings of important confectionery ingredients, cereals and nut products, for example. However, the improvement attained with the use of antioxidants is limited, particularly when the antioxidants are used at levels in conformance with existing food additive regulations published by the Food and Drug Administration.
In the June 1985 article from The Manufacturing Confectioner titled "Antioxidant applications" by Daniel F. Buck, it is noted that in addition to the off-odors and flavors associated with rancidity from oxidation of fats and oils, oxidation can result in color changes, loss of flavor and odor as well as changes in the nutritional quality of food products. For example, when oxidation occurs, fat soluble vitamins such as A, D, and E are destroyed. The caloric content of foods can also decrease and essential fatty acids such as linoleic acid are lost. The article states that oxidation probably affects fats and oils more severely than any other food component or product. The problem is widespread in that, illustratively, many components of confectionery products are high in lipid content and prone to oxidation. Dairy products, fats and oils, nuts, fruits, cereals and essential oils all tend to undergo oxidative deterioration that results in loss of fresh aroma and flavor.
Fish oils are a source of omega 3 long chain fatty acids. Recent research with animals and humans suggests that the omega 3 fatty acids may protect against certain vascular diseases. Experiments on ingestion of omega 3 fatty acids have not been in agreement in this regard. One possible explanation is that in some cases cooking of the fish oil has oxidized the omega 3 fatty acids and reduced or eliminated their alleged protective characteristics.
Heat associated with cooking can promote or catalyze oxidation. Oxidation is typical of most chemical reactions. A 10.degree. C. increase in temperature essentially doubles the reaction rate.
There have been attempts to overcome this problem. For example, in U.S. Pat. No. 3,024,114 a process of preparing fish for canning is disclosed wherein the fish are wrapped in a semi-permeable film prior to a precooking operation with such film restricting evaporation of the natural fish juices during the precooking operation, while restraining direct contact of oxygen or steam with the fish meat. The disclosed process appreciably increases the yield of light-colored meat as compared to existing processes. This process is disadvantageous in that it requires the use of a semi-permeable film and the extra step of wrapping the fish in the film prior to the precooking operation.
U.S. Pat. No. 4,244,979 relates to an oven-type apparatus and method for holding and cooking food. The food is located in inner means with restrictive louvered slots constructed and arranged to provide for additional moisture exchange and/or additional heat exchange between an outer stream of circulating air and the inner core of stable air surrounding the food within the inner means, but without any significant amount of air flow in direct contact with the food for obtaining a fresh-cooked taste, fragrance and appealing appearance of the food. The patentee is not concerned with lipid deterioration, but rather with closely controlling the cooking through the use of uniform temperatures and control of the moisture.
A method of flameless broiling or baking greasy meat products is disclosed in U.S. Pat. No. 4,366,177. In order to avoid flaming or flaring of grease or grease vapors during broiling, the meat products are broiled in a tunnel oven. The vapors produced during cooking including steam, grease vapor and other vaporized volatile constituents produced within the tunnel are selectively vented to remove only an excess of these products of heating. A very slight overpressure of these vapors then exists in the tunnel as an oxygen-starving atmosphere which inhibits burning or flaring up of the grease or grease vapors during broiling. The patentees do not address the problem of preventing lipid degradation or change through exposure to oxygen.
It is known to package food in a vacuum or protective gas to inhibit botulism. For example, U.S. Pat. No. 3,773,527 discloses a method of preserving cooked potatoes wherein peeled, cooked and cut fresh potatoes are preserved in a sealed refrigerated container filled with a mixture of carbon dioxide and nitrogen. U.S. Pat. No. 3,714,887 is for an apparatus for crushing fruit in an inert gas, for example, carbon dioxide or nitrogen, for maintaining the fruit out of contact with oxidizing air. U.S. Pat. No. 2,739,522 is for an apparatus for deaerating and storing oxidizable material. Storage tanks filled with non-oxidizing gas are employed. These patents do not relate to cooking and, in particular, are not concerned with degradation or change of lipids in food during cooking.